A major barrier to the maneuverability of mobile robots is the inadequate performance of available power supplies. Mobile robots generally require a long-term stable power supply for the normal-load operation of robot control electronics and hydraulic and mechanical systems. For many applications of mobile robots additional power is required to satisfy short-term, high-load functions such as high-speed effector positioning, high-torque mobility and high speed propulsion.
One such application is fire fighting. This typically involves passing an extinguishing fluid to a mobile robot through a hose and expelling it through a nozzle towards a fire at a relatively high velocity and volume. The fluid which is forced through the hose to be directed towards a fire is typically water and AFFF, CO2 or Halon and Nitrogen. Once activated, the robot can be preprogrammed to detect intense heat and to direct the flow of extinguishant towards the hottest-point, or the robot can be maneuvered and controlled by personnel from a distance using a radio-controlled device. Fire fighting robots require both long term and high-load power.
Another application involves robots for underwater maneuvers for use during hazardous testing and exploring and rescue missions which typically take place in the oceans. These robots are usually powered by an electric umbilical or an on-board battery and are controlled by sonic transmission or by way of additional wires within the umbilical. Long-term power is desired.
Another application involves the handling of heavy loads which are potentially dangerous in themselves, such as toxic chemicals or explosives. These mobile robots have high power requirements and a long term power supply is desired.
In the field of mobile robots, conventional power sources are generally either of two types; self-contained on-board power units (such as batteries) and remote (non-mobile) power supplies which feed the necessary power to the robot through an electric umbilical cord.
Conventional on-board power supplies include various types of batteries (such as lead acid, NiCad, silver zinc, carbon and mercury), fuel cells, internal combustion engines, gas turbines, thermal batteries, pressurized gas accumulators, photovoltaic cells, mechanical potential systems (such as springs) and thermopile systems involving hydrocarbon or nuclear energy inputs.
The problems associated with these power sources include: inadequate long-term power and/or peak power capacity, poor power to weight ratio and/or excessive bulk, excessive cost, poor shelf life, and possible personal safety hazards. For example, if on-board batteries were used to power a fire fighting mobile robot, although they could provide adequate peak power they would fail to satisfy the long term power requirements and the robot would therefore be unable to fight a fire for long periods of time. The batteries would spend their stored charge and would require time consuming re-charging. Batteries would also have a poor power to weight ratio, a poor shelf life, excessive maintenance requirements and are potentially dangerous if heated due to the fire fighting environment.
Fuel cells could provide long-term low load power, but not short-term high load power. Fuel cells would also be excessively heavy, expansive and also dangerous to operate owing to the combustible nature of the fuels commonly used with them.
Photovoltaic cells, if used would be too expansive, could not effectively provide either long-term low load power or short-term high load power without charging batteries, could be easily damaged, for example, in a fire fighting environment and in some low-light robot applications such as underwater maneuvers these cells would not operate effectively.
Although an electrical umbilical cord could supply the necessary high load and long-term power demands, these cords are vulnerable to damage from the intense heat of a fire fighting environment, corrosion from an ocean environment and deterioration from a chemical environment. A potentially significant personnel hazard exists if an umbilical cord were to leak current. The damaged umbilical could short circuit and spark, possibly creating unexpected fires and explosions in addition to a loss of robot power. Further, these cords are commonly heavy and cumbersome and will restrict the flexible maneuverability of the robot.
Any on-board power generating system involving an isolated on-board supply of combustible fuel such as an internal combustion engine burning diesel fuel or gasoline and thereafter generating the necessary electrical and/or hydraulic pressure requirements posses potential safety hazards if the robot is in a typical fire fighting environment and is not convenient for powering robots in an underwater environment owing to the lack of oxygen available for combustion. Further, these powering systems will only operate for as long as the fuel supply will permit. This could be costly should the fuel supply of such an on-board power generating system be depleted before the operating robot is maneuvered to a position where the fuel supply can be safely replenished. The entire robot could be lost due to inaccessibility or damaged due to extreme heat or underwater pressures if this were to occur while fighting a fire or during underwater maneuvers.